1. Field of the Invention
The present invention relates to an electrophoretic display apparatus and a method of driving the same.
2. Description of the Related Art
An electrophoretic display device is beginning to find application in such fields as electronic book readers, cellular phones, electronic shelf labels, and watches. The electrophoretic display device is capable of display easy on eyes because it can obtain a reflectivity, contrast, and angle of view close to those of paper. Since the electrophoretic display device has a memory property, the device consumes power only for display rewrite, and requires no more power once data is displayed. That is, the electrophoretic display device is a low power consumption display device. The electrophoretic display device also has a structure simpler than that of a liquid crystal display device or an organic electroluminescent display device. Hence, the display device is expected to be more flexible.
An electrophoretic display device using electrophoretic microcapsules disclosed in, for example, Jpn. Pat. Appln. KOKAI Publication No. 2007-507737 is known. The electrophoretic display device disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2007-501737 uses microcapsules in which a dispersant, charged white particles, and oppositely-charged black particles that are charged to a polarity opposite to that of the charged white particles are sealed. In this electrophoretic display device, each microcapsule is sandwiched between electrodes. Jpn. Pat. Appln. KOKAI Publication No. 2007-507737 discloses a technique of making the particles in the microcapsules migrate in accordance with electric fields generated by the electrodes and thus causing the display device to perform black display or white display.
When charged particles and oppositely-charged particles are used as in the technique of the electrophoretic display device disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2007-507737, attractive forces act between the particles. For this reason, the charged particles and the oppositely-charged particles readily cohere. Such cohesion of the particles sometimes leads to mixing of the colors of the charged particles and oppositely-charged particles. The color mixture is not preferable because it lowers the contrast of an image displayed on the electrophoretic display device. When the electric field applied to the electrophoretic display device for black display or white display is changed, the cohered particles sometimes cause an abrupt change of display reflectance. The abrupt change of display reflectance is perceived by the observer as an uncomfortable flicker at times.